How can someone be in a happy relationship yet always crying ir complaining about a ex boyfriend or girlfriend?

I finally got my friend to block her long-time ex boyfriend and deleted all old photos of him. She is now taking a break from social media for 90 days and isn't talking to anyone in our friend group now. She also has been in a happy relationship for 8 months yet seems to always be crying or bring up two of her ex bfs in some way or another.
How can someone be in a happy relationship yet always crying ir complaining about a ex boyfriend or girlfriend?
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